1. Technical Field
Various embodiments presented herein relate to a data storage device, and more particularly, to a method for improving the reliability of a data storage device.
2. Related Art
Computing has become ubiquitous so that computer systems can be used essentially anytime and anywhere. Because of this, the use of portable electronic devices such as mobile phones, digital cameras, and notebook computers has rapidly increased. In general, such portable electronic devices use a data storage device which uses a memory device. The data storage device may be used as a main memory device or an auxiliary memory device of a portable electronic device.
A data storage device using a memory device provides advantages at least because there is no mechanical driving part. As a result, stability and durability are excellent, information access speed is high and power consumption is low. Data storage devices having such advantages include a USB (universal serial bus) memory device, a memory card having various interfaces, and a solid state drive (SSD).
As large capacity files such as music files and video files are reproduced in a portable electronic device, a data storage device is required to have a large storage capacity. In order to secure a large storage capacity, a data storage device includes a memory device with a large number of integrated memory cells, for example, a flash memory device may be used as a nonvolatile memory device.
A flash memory device does not support overwrite due to a structural characteristic. That is to say, memory cells which are programmed cannot be updated with new data until the memory cells are erased. Therefore, in order to program new data to the flash memory device, an erase operation should be carried out prior to writing new data. This is referred to as an erase-before-program operation. In other words, memory cells of the flash memory device which are in the program state should be initialized to an initial state or an erase state before new data are programmed.
However, the erase operation of the flash memory device requires an undesirably long time. For this reason, a controller for controlling the flash memory device preferably does not reprogram data to programmed memory cells. Instead, the controller of the data storage device programs data to memory cells which are recovered to an erase state.
Due to such an operation of the controller of the data storage device, memory cells of the flash memory device store both valid data and invalid data. As the case may be, the controller of the data storage device selectively performs a merge operation to gather valid data to continuous locations and to erase invalid data.